Backfire door



April 16, 1940- J. s. HASBROUCK ,1 7,

BACKFIRE DOOR Filed June 3, 1937 20 %%%%o1 2a I 000000 /0 I r E .2 a 7a2 34 I I I I f "min ,r I) I Mi w r I r W H M7.

IN V EN TOR.

A TTORNEY Patented Apr. 16, 1940 r 1 UNITED STATES PArsNroFFicE toUnited Aircraft Corporation, East Hartford, Conn, a corporation ofDelaware Application June 3,1937,- Serial No. 146,184

a v 7' Claims. (01. 137--53) This invention relates to improvements-inpressure responsive valves and has particular reference to an improvedbackfire door for an engine fuel induction system.

An object of the invention resides in the provision of an. improvedbackfire door the opening of which is always resisted by substantiallythe same force regardless of the pressure-of the sur roundingatmosphere.

A further object resides in the provision of an improved backfire doorwhich will tend to open easily under-the influence of a sudden increasein the pressure in the induction system adjacent to the door opening,but which will remain closed under gradual changes in the ratio of thepressures within and without the fuel induction system.

A still further object resides in the provision of an improved. backfiredoor which is light in weight, simple to manufacture, easy to install,and which will not ordinarily get out of order in use.

Other objects and advantages will be more particularly pointed outhereinafter or will become apparent as the description proceeds.

In the accompanying drawing ln'which like" reference numerals are usedto designate similar, parts'throughout, there is illustrated a suitablemechanical embodiment of what is now considered to be the preferred formof the idea of the invention. The drawing,'how ever, is for thepurposeof illustration only and is not to be taken as limiting the invention,the'scope of which is to be measured entirely by the scope. of theappended claims. I v

Inthedrawing l Fig.1'is' a schematic elevational view of an internalcombustion engine and a fuel induction system therefore showing theapplication thereto of the device of the invention.

- Fig. 2 is a sectional view on an enlarged scale of the improvedbackfire door showing in detail the construction thereof. I I

Referring to the drawing in detail the numeral Ill generally indicatesan internal combustion engine of a type ordinarily employed for thepropulsion of aircraft. It is to be understood, how-' ever, that thedevice of the invention is not limited to any particular type ofinternal combustion engine.

The engine is provided with a crankcase I2 supporting a plurality ofcylinders, as indicated at ,to the combustion chambers of which fuel isled throughthe intake manifolds l6. In the form of engine illustrated,the ends of the in-.

take manifolds Hi opposite the cylinder connected ends are connected toa power driven supercharger" l'B, which' will hereinafter be re? ferredto as the primary supercharger. A carburetor 20 is connected to thecentrally located "5' inlet opening of the supercharger l8 by a suitableduct'22 for supplying a combustible mixture of fuel and air to theengine. In the arrangement illustrated a second supercharger 25, whichwill hereinafter be referred to as the aux- 10 iliary supercharger, orauxiliary stage, is connected to the carburetor by a suitable air duct26 within which there is disposed a radiator or intercooler 28. Theauxiliary supercharger 24 may receive air from, the atmosphere through asuitable duct or scoop 3%). As is well-known in the aircraft art, thepressure and density of the atmosphere varies with altitude and anairplane engine is forced to operate at different atmospheric pressures,depending on the flight altitude D of the airplane on'which it ismounted, to the material detriment to the efiicient operation of theengine, unless some means are provided to maintain the pressure in theengine fuel induction system substantially constant. Means for 5maintaining the pressure in the engine fuel induction systemsubstantially constant are known to the art and an example'of such anarrangement is illustrated and described in detail in application Ser'.No. 133,160 of Wright, A. Perkins, l0 filed March 26, l93'Z,'for Twostage supercharger.

In the illustrative arrangement of an engine fuel induction system shownin Fig. 1, the pressureof the fuel mixture supplied to the cylinder.

' is brought up to a desired'predetermined value '5 by the action of thesuperchargers i8 and 24, and

is prevented from exceeding the desired value .by suitable throttlingmeans applied to the carburetor2ll, so that the pressure of the airinthe interior of the carburetor 29 is maintained sub 40 stantiallyconstant at a predetermined value.

It has been found that with previous backfire door constructions, if aconstant pressure is maintained in the carburetor, the resistance of thebackfire door to opening changes with the change is in the pressure ofthe surrounding atmosphere so that if suflicient spring resistence isprovided to maintain the door tightly closed at very low atmosphericpressures incident to operation at high altitude, at low alatitude theresistence of the door to opening will be so great that there will bedanger of a backfire in the carburetor failing to open the backfire doorandfinding its way out of the engine fuel induction system by disruptingthe air ducts or the intercooler, if one is protively delicate structurecomposed of thin tubes and sheet metal chambers soldered together, it

may be consideredas one of the objects of this invention to provide abackfire door which will,

at all times protect such an intercooler against disruption due toexcessive pressures incident to backflring of the engine. I

Referring to Fig. 2 the carburetor 20, or the air duct leading to theengine, forming in efiect.

with a backfire door 1 tional force will be required to open the door agas container, is provided supporting rib 32, extending the backfireaperture designed as a circular port in the bottom wall, or other outerwall, of the carburetor. v

A tubular stem 36 is secured to the rib 32 by diametrically acrosssuitable means such as the screw threaded connection 38, in such amanner that it projects downwardly concentric with the aperture 34, and

terminates below the bottom wall of the carburetor or duct. A disk 40 issecured upon the bot- .tom end of the stem 36 by suitable means such asthe nut 42 and shoulder 44, and with a peripheral packing ring 46.

The backfire door itself is in the general form of an inverted cupshaped member 48, provided in its closed end with a concentric aperturethrough which the pin 36 extends, and having its open end overlying theperiphery of the disk 40 and the packing ring 46. The member 48 isresiliently held in its uppermost position by a coiled compressionspring 50 disposed between the disk 40 and an abutment 52 slidablymounted on the stem 36 and is provided around the periphery of itsclosed end with an annular bead 54 which cooperates with a gasket 56 toseal the aperture 34 when the door 48 is in its uppermost position.

By-reason of the above described shape and arrangement of the parts aclosed chamber 58 is provided between the interior of the cup shapeddoor member 48 and the disk 40. This chamber is connected with theinterior of the carburetor by means of port 60 leading from the interiorof the tubular stem 36, the upper end of which is in communication withthe interior of the carburetor and the lower end of which is made solidat and below the shoulder 44. The passage through the stem 36constitutes an orifice for controlling the rate of flow of fluid intothe chamber 58. With this arrangement of the parts the air pressurewithin the chamber 58 is normally the same as the fluid pressure withinthe carburetor regardless of the pressure of the surroundingatmosp-here,but its rate of change in response to. pressure changes in thecarburetor is controlled by a degree of restriction of the abovementioned orifice.

When a backfire occurs, the door'member 48 is moved downwardly to openthe port 34 and is moved downwardly against the substantially constantfluid pressure in the chamber 58 so that the door always opens with thesame force. 3

In order to avoid compression of the fluid in the chamber 58 theinterior wall of the cylindrical portion of the door member 48 isprovided with grooves 62 separated by parallel longitudinally extendingridges 64. As soon as the lower ends of the grooves 62 have passed theperipheral extent of the disk member 40, the chamber 58 is connectedwith the external atmosphere and the only resistance to the downwardmovement of the door is the force of the spring 50. As soon as theexcess pressure incident to the backfire has been vented, the spring 50forces the door member upwardly to its closed position and is provided34 which is conveniently; I

pressure relief the pressure in the chamber 58 is again imme- 1 diatelyequalized to the pressure existing in the interior of the carburetor.

If desired, the backfire door may be surrounded by a cover member 66which may be provided with i an open flared end to deflect the backfireblast away from the carburetor,-ormay be connected with a tail pipeleadin retor .1

When the pressure of the external atmosphere is above the pressure inthe carburetor, no addisince the pressure in the chamber 58 will be beelow the atmospheric pressure and the same as the pressure in thecarburetor, similarly when the M away from the carbuatmospheric pressureis below the pressure in the carburetor, the force required to openthejdoor 'is not changed, since the pressure in the chamber 58 is thenabove the atmospheric pressure and equal" to the pressure in thecarburetor. From the above consideration it will be observed that theforce required to open the backfire door is substantially constantregardless of variations in the pressure of the surrounding atmosphere.

While there has been illustrated ,and described a suitable mechanicalembodiment of what is now consideredto be the preferred form of the ideaof the stood that the invention is not limited to the construction soillustrated and described but-that such changes in the size, shape andarrangement invention, it is to be under of parts may be resorted to ascome within the scope of the appended claims; 7

Having now described the invention so that others skilled in the art mayclearly understand the same, what it vis desired to secure by. LettersPatent is as follows:

1. A backfire doorincluding a movable'closure member responsive to'sudden increasesin fluid pressure on one sidethereof to move to openposition, a spring urging said closure memberhto closed position, avariable volume chambery at the opposite-side of said closure member,means connecting said chamber with the fluid pressure at said one sideof said closure member to main-' tain in said .;cham,ber .a fluidpressure effective to balance the'fiuid pressure tendingtoinove saidclosure member to open positionsaid means including an orifice forrestricting the flow of fluid to said chamber to retard the charges ofpressure in-said chamber and provide an interval of unbalanced pressureon the opposite sides of said closure member when the increaseof fluidpressure tending to move said closure member to open position takesplace at a speed above a prede--.

termined rate, and a normallyv closed vent for said chamber largerthansaid orifice opened by initial opening movements of said'clo'suremember, wherebysaid closure member will move ,to.

open position inrespons'e' in said fluid pressure but gradual.

2. A backfire door to a sudden increase. will remain inv closed positionwhen the increase in fiuidpressure'isfor an enginefuelsystem including afuel mixture duct and an-intercooler comprising, a relatively lightmovable closure member for mounting in covering relation with aaperture, a chamber at the .side

of said closure member opposite said aperture,

means for connecting said chamber with the fluid pressure on the side ofthe closure member oppo site said chamber for balancing-the fluidpressures-on the opposite sides of said closuremember, said meansincluding a restricted orifice for maintainingusaid. pressuresunbalanced under ing substantially equal areas on opposite sidessuddenincreases in the fluid pressure on the side of the closure memberopposite the chamber, a normally closed vent for said chamberlarger-than said orifice opened by initial opening movements of saidclosure member, and a light spring constituting normally the onlyunbalanced force urging said closure member to aperture coveringposition. I

3. In a pressure actuated valve, a member having substantially equalareas on oppositesides thereof actuatable by fluidpressure on onesidethereof to open said valve, a pressure chamber on each side of saidmember, means for conducting fluid under pressure from the chamber atone side of said member to the chamber at the opposite side thereof toovercome the effector fluid pressure on one side of said member tendingto open said valve, saidmeans including an orifice for restricting theapplication of fluid pressure to, said opposite side of said member,said chamber at said opposite side of said member having an outlet of anarea substantially unrestricted in comparison with the area of saidorifice opened by an initial opening movement of said member.

. 4. In a pressure actuated valve, a member havthereof actuatableby'fluidpressure on one side thereof to open said valve, a variablevolume fluid pressure chamber on the opposite side of said memberadapted to contain a compressible fluid, a spring in said chamber forresiliently urging said member to valve closing position, means forsupplying fluid pressure to said variable volume chamber to overcome theeffect of fluid pressure on said one side of said member tending to opensaid valve, said means including an orifice for restricting theapplication of 'fluid pressure to said 'varable volume chamber tomaintain the pressure changes in said variable volume chamber at arate'below the rate of increase of pressure applied to said one side ofsaid member when such rate of pressure increase is above a predeterminedvalue, said chamber including passages for relieving fluid pressuretherefrom once said valve member has been moved a predetermined amountagainst the force exerted by the compressible fluid in said chamber. f

5. A'backfire door for an internal combustion engine carburetorcomprising, a supporting housing for said door, a stem projectingoutwardly" from said housing, a cup shaped door member slidably mountedon said stem in position tov cover a vent opening in said housing, aclosure member for the open end of said door member rigidly mounted onsaid stem, a spring supported by said stem for urging said door memberto aperture closing position, a fluid passage extending through saidstem to. the space between said door member and said closure membenand aI fluid passage controlled by said door member for venting said spacewhen said door member moves I to open said vent opening.

6. A backfire door for an internal combustion engine carburetorcomprising, a hollow stem secured at one end concentrically of a ventopening in a supporting housing, a disc, secured upon the other end ofsaid stenna cup shaped door member slidably mounted on said stem inposition to normally close said stem opening, said door memher having anannular Wall surrounding said disc to provide a closed chamber withinsaid door member, a spring in said chamber holding said door member tovent closing position, a fluid channel extending through said stem fromthe interior of said housing to the interior of said chamber, and one ormore fluid channels in said door member opened by an initial openingmovement of said door member to vent saidchamber to the atmosphere,

'7. In a' pressure relief device for a'gas con-- tainer, a valvenormally closing an orifice in said container, means resiliently urgingsaid valve to and normally holding said valve in closed position, meansincluding a fluid passage with a re-. stricted orifice connecting theinterior of said container with a chamber on the opposite side of saidvalve for normally equalizing the pressure on opposite sides of saidvalve to render said resilient means effective to maintain said valve 7

